U.S. patent number 4,593,783 [Application Number 06/727,079] was granted by the patent office on 1986-06-10 for power steering system.
This patent grant is currently assigned to Toyoda Koki Kabushiki Kaisha. Invention is credited to Susumu Honaga, Yoshiharu Inaguma, Mikio Suzuki.
United States Patent |
4,593,783 |
Honaga , et al. |
June 10, 1986 |
Power steering system
Abstract
A power steering system which includes an engine-driven pump, a
fluid motor for supplementing manual steering torque, a fluid
control valve for distributing fluid to the fluid motor, and a
reaction device for applying hydraulic reaction or feeling to a
steering wheel. A first flow control valve is utilized to deliver
first fluid flow to a fluid control valve from the pump and to lead
excess flow to a bypass passage. A second flow control valve is
connected between the bypass passage and the reaction device to
deliver second fluid flow to the reaction device and to lead excess
flow to a reservoir. A magnetic pressure control valve is connected
to the reaction device to control fluid pressure applied thereto in
accordance with a predetermined vehicle operating condition, such
as vehicle speed.
Inventors: |
Honaga; Susumu (Aichi,
JP), Suzuki; Mikio (Hekinan, JP), Inaguma;
Yoshiharu (Nagoya, JP) |
Assignee: |
Toyoda Koki Kabushiki Kaisha
(Kariya, JP)
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Family
ID: |
13908840 |
Appl.
No.: |
06/727,079 |
Filed: |
April 25, 1985 |
Foreign Application Priority Data
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Apr 27, 1984 [JP] |
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59-87221 |
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Current U.S.
Class: |
180/421; 91/446;
91/451 |
Current CPC
Class: |
B62D
6/00 (20130101) |
Current International
Class: |
B62D
6/00 (20060101); B62D 005/08 () |
Field of
Search: |
;180/142,141,143,132,146,147,149,133
;91/446,468,451,450,452,371,372 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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821944 |
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Oct 1959 |
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GB |
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2131364 |
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Jun 1984 |
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GB |
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Primary Examiner: Love; John J.
Assistant Examiner: Diederiks, Jr.; Everett G.
Attorney, Agent or Firm: Oblon, Fisher, Spivak, McClelland
& Maier
Claims
What is claimed as new and desired to be secured by Letters Patent
of the United States is:
1. A power steering system which utilzies a fluid pump driven by a
drive source and a fluid motor for supplementing manual steering
torque, comprising:
a valve housing;
a rotatable output shaft partially positioned within said valve
housing and operatively connected with said fluid motor;
a rotatable input shaft partially positioned within said valve
housing and aligned with said output shaft and adapted for manual
actuation;
rotary fluid control valve means located in said valve housing for
distributing fluid flow to said fluid motor in accordance with
relative rotation between said input and output shaft;
a reaction device located in said valve housing for providing
resistance against relative rotation between said input and output
shaft in accordance with fluid pressure supplied thereto;
first flow control valve means connected between said fluid pump
and said rotary fluid control valve means for delivering a first
fluid flow to said rotary fluid control valve means and for leading
excess flow to a bypass passage;
second flow control valve means connected between said bypass
passage and said reaction device for delivering a second fluid flow
to said reaction device and for leading excess flow to a reservoir;
and
magnetic pressure control valve means connected to said reaction
device for controlling fluid pressure applied thereto in accordance
with a predetermined vehicle operating condition.
2. A power steering system as set forth in claim 1, further
comprising a torsion bar which interconnects said output shaft and
said input shaft.
3. A power steering system as set forth in claim 1, wherein said
reaction device further comprises:
a reaction force chamber formed on said output shaft in coaxial
relation therewith;
a reaction force receiver formed on said input shaft and rotatably
housed in said reaction force chamber;
a reaction piston received in said reaction force chamber so as to
be prevented from relative rotation therewith and which is adapted
to be urged toward said reaction force receiver by fluid pressure
applied thereto; and
engaging means engageable with both said reaction force receiver
and said reaction piston.
4. A power steering system as set forth in claim 1, wherein said
reaction device further comprises:
a reaction force cylinder radially formed on said output shaft;
a plunger slidably mounted in said cylinder and adapted to be urged
toward said input shaft by fluid pressure applied thereto; and
engaging means formed on said input shaft for engaging with said
plunger.
5. A power steering system which utilizes a fluid pump driven by a
drive source and a fluid motor for supplementing manual steering
torque, comprising:
a valve housing;
a rotatable output shaft partially positioned within said valve
housing and operatively connected with said fluid motor;
a rotatable input shaft partially positioned within said valve
housing and aligned with said output shaft and adapted for manual
actuation;
rotary fluid control valve means located in said valve housing for
distributing fluid flow to said fluid motor in accordance with
relative rotation between said input and output shaft;
a reaction device located in said valve housing for providing
resistance against relative rotation between said input and output
shaft in accordance with fluid pressure supplied thereto;
first flow control valve means connected between said fluid pump
and said rotary fluid control valve means for delivering a first
fluid flow to said rotary fluid control valve means and for leading
excess flow to a bypass passage;
second flow control valve means connected between said bypass
passage and said reaction device for delivering a second fluid flow
to said reaction device and for leading excess flow to a reservoir;
and
magnetic throttle valve means connected to said reaction device and
including means for varying the area of a throttle portion of said
throttle valve in accordance with a predetermined vehicle operating
condition.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a power steering system wherein
power assistance derived therefrom will be modulated according to a
vehicle condition such as vehicle speed.
2. Description of the Prior Art
In maneuvering a steering wheel of an automotive vehicle, it is
recognized that power assistance at high vehicle speeds may
desirably be less than at low speeds to allow for stabilization of
the steering wheel at high speeds.
A power steering system with the above-mentioned steering
characteristics is known having a reaction device that is supplied
with a fluid pressure which is increased as the vehicle speed
increases, thus applying a hydraulic reaction or feeling to the
steering wheel. In such prior system, an additional fluid pump
which is driven at a rate proportional to vehicle speed is provided
to supply the reaction device with fluid pressure proportional to
vehicle speed. As a result, it is difficult to control the pressure
of the fluid as freely as desired or according to other vehicle
conditions such as rotational angle and rotational speed of the
steering wheel.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a
power steering system, wherein the pressure of the fluid that is
supplied to the reaction device may easily be controlled as
desired.
Another object of the present invention is to provide a power
steering system having the foregoing desirable characteristics and
which is of simple construction and is relatively inexpensive.
Briefly, according to the present invention, these and other
objects are achieved by providing a power steering system including
an engine-driven pump, a fluid motor, a rotatable output shaft
operatively connected with the fluid motor, a rotatable input shaft
adapted for manual actuation, a fluid control valve for
distributing fluid flow to the fluid motor in accordance with
relative rotation between the input and output shafts, and a
reaction device for providing resistance against relative rotation
between the input and output shafts. A first flow control valve is
provided which is connected between the pump and the fluid control
valve to deliver a first fluid flow to the fluid control valve and
to lead excess flow to a bypass passage. A second flow control
valve is connected between the bypass passage and the reaction
device to deliver a second fluid flow to the reaction device and to
lead excess flow to a reservoir. A magnetic pressure control valve
is connected to the reaction device to control fluid pressure
applied thereto in accordance with a vehicle condition such as
vehicle speed.
BRIEF DESCRIPTION OF THE DRAWINGS
Various other objects, features and attendant advantages of the
present invention will be more fully appreciated as the same
becomes better understood from the following detailed description
when considered in connection with the accompanying drawings in
which like reference characters designate like or corresponding
parts throughout the several views and wherein:
FIG. 1 is a longitudinal sectional view of a power steering system
according to the present invention;
FIG. 2 is an enlarged sectional view taken along line II--II of
FIG. 1;
FIG. 3 is a longitudinal sectional view of the magnetic pressure
control valve shown in FIG. 2;
FIG. 4 is a graph showing fluid pressure controlled by the magnetic
pressure control valve as a function of current applied thereto;
and
FIG. 5 is a fragmentary longitudinal sectional view of a second
embodiment of a power steering system according to the present
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to the drawings and to FIG. 1 in particular, reference
numeral 10 designates a gear housing that is fixedly mounted on a
chassis of an automotive vehicle. A steering rod 14 is slidably
mounted on gear housing 10, with opposite ends thereof extending
outwardly from gear housing 10. Respective ends of steering rod 14
are connected to steerable wheels of the vehicle by way of a
conventional steering link mechanism. A piston 15 of a fluid motor
is fixedly attached to a middle portion of steering rod 14 and is
slidably accommodated in a cylinder tube 16 that is unitarily
connected to gear housing 10.
Referring now to FIG. 2, an output shaft 11 is rotatably journalled
to gear housing 10 in perpendicular relation with steering rod 14.
A pinion is provided on output shaft 11 and is engaged with a rack
14a which is formed on steering rod 14.
A valve housing 18 is fixedly attached to gear housing 10 and
accommodates a rotary fluid control servo-valve 20 which comprises
a sleeve valve member 21 and a rotary valve member 22. Sleeve valve
member 21 is rotatably housed in valve housing 18 in coaxial
relation with output shaft 11. Rotary valve member 22 is formed on
an input shaft 24 which is connected to a steering wheel. Input
shaft 24 is flexibly connected to output shaft 11 by means of a
torsion bar 25. Loose engagement of toothed portions 23 of output
and input shaft 11 and 24 permits a small amount of relative
rotation therebetween. A plurality of axially extending slots 21a,
22a are formed on an internal surface of sleeve valve member 21 and
on a circumferential surface of rotary valve member 22 at regular
intervals. Thus, according to the relative rotation between sleeve
valve member 21 and rotary valve member 22, a supply port 26
communicates with one of cylinder ports 28, 29 which are
respectively in fluid communication with left and right chambers
16a, 16b of the fluid motor, and an exhaust port 27 communicates
with the remaining port of cylinder ports 28, 29.
A cylindrical portion 30 is formed at an inner end of output shaft
11 and is rotatably received in valve housing 18. Output shaft 11
is connected to sleeve valve member 21 at the end of cylindrical
portion 30 by means of a connecting pin 31. A reaction force
chamber 33 of a reaction device is formed on cylindrical portion 30
in coaxial relation with output shaft 11. A flange shaped reaction
force receiver 34 is provided on input shaft 24 and is rotatably
housed in reaction force chamber 33.
A ring shaped reaction piston 35 is axially slidably received in
reaction force chamber 33 in face to face relationship with
reaction force receiver 34. Reaction piston 35 is prevented from
rotation relative to output shaft 11 by means of a pin 38. An inner
bore of reaction piston 35 is slidably fitted on input shaft 24 and
thus, reaction piston 35 divides reaction force chamber 33 into
left and right chambers 33a, 33b. The left chamber 33a is led to a
port 40 to which controlled fluid pressure is introduced as
described hereinafter. The right chamber 33b is led to a port 41
that is connected to a reservoir. On opposite faces of reaction
force receiver 34 and reaction piston 35, four pairs of conical
shaped notches 34a, 35a are formed with the same circumferentially
interval. Placed between reaction force receiver 34 and reaction
piston 35 is a retainer 37 which receives four balls 36 that
respectively engage with conical shaped notches 34a and 35a.
Reaction piston 35 is urged toward reaction force receiver 34 by a
wave spring 39 that is disposed between reaction piston 35 and a
bottom wall of reaction force chamber 33.
Reference numeral 50 designates a pump that is driven by an engine
of the vehicle. An outlet port 50a of pump 50 is connected to
supply port 26 of servovalve 20 by way of a first flow control
valve 51. First flow control valve 51 includes a metering orifice
52 which is interposed in a conduit 45 that connects outlet port
50a of pump 50 with supply port 26, and a bypass valve spool 54
that is moved in accordance with the pressure differential across
metering orifice 52 so as to keep the pressure differential
constant. Thus, a first fluid flow of a sufficient and constant
rate is delivered to supply port 26, and any existing excess flow
is led to a bypass passage 53 according to the function of flow
control valve 51. Bypass passage 53 of first flow control valve 51
is connected to port 40 of reaction force chamber 33 by way of a
second flow control valve 55. Second flow control valve 55 also
includes a metering orifice 56 which is interposed in a conduit 46
that connects bypass passage 53 with port 40, and a bypass valve
spool 58 that is moved in accordance with the pressure differential
across metering orifice 56 so as to maintain the pressure
differential constant. According to the operation of second flow
control valve 55, a second fluid flow of a constant rate is
delivered to port 40, and any existing excess flow is led to a
reservoir by way of bypass conduit 57. A magnetic pressure control
valve 60 is connected to port 40 of reaction force chamber 33.
Referring now to FIG. 3, magnetic pressure control valve 60 is
provided with a valve body 62 which is attached to housing 61, and
a solenoid 63 that is secured to valve body 62. A spool member 64
which is adapted to be moved according to excitation of solenoid 63
is slidably accommodated in valve body 62. A valve seat member 66
which is secured to housing 61 is provided with a relief passage 65
that is connected to port 40 of the reaction device. A ball valve
67 which is engageable with valve seat member 66 to close relief
passage 65 is urged toward valve seat member 66 by a spring 68 that
is interposed between ball valve 67 and spool member 64. Spool
member 64 is counterbalanced by a balance spring 69 and is usually
maintained at the position shown in FIG. 3 where the force of
spring 68 applied on ball valve 67 is maximum. The force of spring
68 will be reduced as spool member 64 is moved against balance
spring 69 according to the excitation of solenoid 63. Solenoid 63
is connected to a solenoid drive circuit 71 which in turn is
controlled by a computer 70. Current I which is supplied to
solenoid 63 is controlled by computer 70 so as to decrease as the
vehicle speed V increases. In addition, when current I increases,
controlled pressure Pc in relief passage 65, namely, the pressure
applied to the reaction device decreases, as shown in FIG. 4.
A magnetic throttle valve 60a which is operative to vary the area
of a throttle according to current supplied to a solenoid thereof
controls pressure Pc as a function of the current as shown in FIG.
4, and may be substituted for magnetic flow control valve 60.
The operation of the power steering system as described above will
now be explained. Fluid flow discharged from pump 50 is divided
into a first fluid flow of constant rate and an excess flow by
first flow control valve 51. The first fluid flow is delivered to
supply port 26 of servo-valve 20 to be distributed to the fluid
motor. The excess flow is also divided into a second fluid flow of
constant rate and an excess flow which is bypassed to the
reservoir. The second fluid flow is delivered to port 40 of the
reaction device and is led to the reservoir by way of magnetic
pressure control valve 60. While the vehicle speed is low, the
force of spring 68 is null because a maximum current I is supplied
to solenoid 63. Therefore, controlled pressure Pc, namely, the
pressure in the left chamber of reaction force chamber 33 is kept
substantially null, and, in turn, reaction piston 35 is urged
toward balls 36 only by the resilient force of wave spring 39.
Thus, when input shaft 24 is turned according to manual maneuvering
of the steering wheel, reaction piston 35 is easily retracted
against wave spring 39, resulting in easy relative rotation between
sleeve valve member 21 and rotary valve member 22 in a usual power
assisted steering operation.
When the vehicle speed is above a predetermined rate, computer 70
controls solenoid drive circuit 71 in accordance with a signal
corresponding to vehicle speed V so that current I supplied to
solenoid 63 of magnetic pressure control valve 60 decreases as
vehicle speed increases. Therefore, when the vehicle speed
increases, the force of spring 68 increases proportionately, and,
in turn, the pressure applied to the left chamber of reaction force
chamber 33 increases correspondingly. Thus, reaction piston 35 is
urged toward balls 36 with a thrust force corresponding to
controlled pressure Pc. Such increases the manual torque which is
necessary to generate relative rotation between sleeve valve member
21 and rotary valve member 22 and, as a result, produces less power
assistance at higher vehicle speeds than at lower speeds.
Another example of a reaction device is shown in FIG. 5, wherein
four reaction force cylinders 80 are radially formed at a
cylindrical portion 81 of output shaft 11 at the same
circumferentially interval. Four V-shaped grooves 82 are formed on
an exterior surface of input shaft 24 opposite to reaction force
cylinders 80. Plungers 83 which are slidably mounted in respective
cylinders 80 include balls 85 which engage with grooves 82
respectively. An annular groove 86 is provided on an outer surface
of cylinder portion 81 to communicate reaction force cylinders 80
with port 40 to which controlled pressure Pc is supplied.
Although in the above-described embodiments, reaction force
cylinders 33 or 80 are formed on a cylindrical portion of output
shaft 11, the same effect as in the above-described embodiments can
be obtained in the case where the reaction force cylinders are
formed on a sleeve valve member.
Furthermore, should it be required, controlled pressure Pc supplied
to the reaction device might be controlled according to another
vehicle condition such as the rotational angle or rotational speed
of the steering wheel or a desirable combination of selected
vehicle conditions.
Obviously, numerous modifications and variations of the present
invention are possible in light of the above teachings. It is
therefore to be understood that within the scope of the appended
claims, the invention may be practiced otherwise than as
specifically described herein.
* * * * *